The invention related to an assembly of a valve unit, a combustion air intake and an exhaust gas recirculation unit for an internal combustion engine.
A valve unit for use in an exhaust-gas return unit is known, for example, from European Patent A2 900930. The valve unit therein is provided with a drive unit, a gear mechanism, a valve rod and at least one valve disk, the gear mechanism being provided with an eccentrically disposed coupling which is connected coactingly with the valve rod. Rotary movements of the motor and of the gear mechanism connected thereto can be transformed in simple manner to linear movements of the valve rod with large positioning force by such an eccentric arrangement of the coupling. Because the valve rod is fixed on the coupling in this case, however, relatively large friction forces must be overcome, thus making it difficult, because of the slewing movement of the valve rod, to achieve positioning of the valve element.
An object of the invention is to provide a valve unit of the above type for internal combustion engines, which avoids the aforesaid disadvantages and in addition can be manufactured inexpensively with simple construction.
This object is achieved in that the coupling comprises a bearing element which serves as a connection means with the valve rod.
In this way, it is ensured that straight, linear movement of the valve rod takes place despite the eccentricity of the coupling. Moreover, frictional losses are limited to a minimum. A particularly simple and robust embodiment of the valve unit can be achieved by constructing the bearing element as a roller bearing. The gear mechanism can then be provided with a guide member which has cam elements acting on the roller bearing, one in the vertical direction and the other in the horizontal direction, the guide member being fixed to the valve rod, whereby the valve rod and thus also the valve disk attached thereto, by virtue of the horizontal cam element, can also be moved in closing direction in response to reversal of the direction of rotation of the drive unit. In this respect, the vertical cam element functions as an end stop for the roller bearing if it were to exceed the maximum stroke (or angle of rotation). In this way, it is possible to achieve motor-assisted closing and retaining forces, which can prevent unwanted opening of the valve when it is used, for example, as an exhaust-gas return valve. Moreover, critical operating conditions such as seizing or sticking of the valve disk can be overcome. For automatic restoration of the valve disk to closed position, a spring element is provided which applies tension on the valve rod in the direction of the roller bearing.
A gear mehanicm comprising a planetary gear mechanism or planetary stationary gear mechanism is particularly advantageous for compact construction of the valve unit. In particular, the planetary stationary gear mechanism allows a short overall length of the gear mehanicm, with the accompanying result that reduced inertia as well as low friction result in higher efficiency of the gear mehanicm.
A valve unit which is simple to assembly is obtained in that there is provided a cover element, which is equipped with a connection plug for establishing electrical contact and which has plug contact elements which engage complementary plug contact elements of the drive unit when the cover element is mounted in place, thus establishing an electrical connection to the drive unit. In a particularly advantageous embodiment, there is provided a sensor for sensing the position of the valve stroke, the sensor being designed such that it can be electrically connected to the connection plug. The sensor can be comprised of a diametral annular magnet and a Hall-effect sensor element. Thus, a ring gear of the planetary or planetary stationary gear mechanism can be disposed in the annular magnet. There can also be provided an on-board electronic module for system control.
From the viewpoint of assembly, it is particularly advantageous to dispose the drive unit and the gear mechanism unit in a tunnel housing.
The valve unit of the invention is suitable in particular for use in the exhaust-gas return line of an internal combustion engine. In a valve unit for exhaust-gas return as disclosed, for example, in German Patent A1 4338192, the valve rod projects directly into the air intake tube, and extreme fouling can occur because of the contact of the cold fresh air with the hot exhaust gas. This disadvantage is avoided in a combustion-air intake-channel portion in which the exhaust-gas inlet portion is provided with a discharge portion, which is disposed coaxially relative to the intake-channel portion and which, via a connecting channel disposed transversely relative to the discharge portion, is connected to a valve-channel portion, which is intersected by the connecting channel, the connecting channel being provided with an outwardly projecting channel attachment, which is closed by a plug type insert. This valve-channel portion can form a connecting nozzle for an exhaust-gas return line, and this connecting nozzle can also be provided with the valve seat.
Also provided in accordance with the invention, is an exhaust-gas return unit with a valve unit and a combustion-air channel portion, in which the valve rod extends into a valve guide bushing, which at one end projects into the valve-channel portion and at the other end into a valve spring chamber. In this case it is advantageous for the valve rod, on the portion which projects into the valve spring chamber, to support the guide member, which bears on one end of the spring element whose other end is braced against the wall of the valve-spring chamber. The valve-spring chamber can be closed off from the outside by the housing for the gear mechanism and drive unit. The valve guide bushing can be provided with a dirt chamber, which is formed, for example, by a bore in the housing. In order to achieve an advantageous exhaust gas return, the valve disk can be provided with a cylindrical portion extending downstream from the valve seat. In order to be able to use a smaller valve disk, which in turn permits smaller positioning forces, the valve disk can be provided with a tapered edge, which cooperates with a taper portion of the valve seat and located downstream from the line of contact to form a diffusor portion. A throttle valve can be disposed in the intake-channel portion, upstream from the discharge portion. To achieve a construction which saves as much space as possible, the combustion-air intake-channel portion can be integrated with the housing of the gear mechanism and drive unit.